The extra-cellular volume of female Sprague-Dawley rats was expanded by 20 percent with either NS or D5W over a period of one hour. At this point the infusion was either stopped or continued to match urinary output. In other studies, total body sodium was increased by 15 percent without concomitant volume expansion, through the use of 3 percent saline, and hyperoncotic albumin infusions were performed in rats undergoing a saline diuresis. The purpose of these manipulations was to evaluate the role of the kallikrein system in adaptation to acute alterations in extra-cellular volume and salt concentrations. Urine was collected over timed periods and tested for (Na), (K), and kallikrein. A radioimmunoassay was used to measure kallikrein. Initial results reveal changes in kallikrein during expansion. The relationship of kallikrein to the other measured variables is not clear at this time.